Suspension or liquid dispersion systems in which fine particles are dispersed in a continuous-phase solvent are divided into the following two categories according to shear rate characteristics: Newtonian fluids that show a constant viscosity regardless of a change in the shear rate; and non-Newtonian fluids whose viscosity changes when the shear rate changes.
A shear thickening fluid (STF), a kind of non-Newtonian fluid, is a fluid such as a colloidal suspension which contains solid particles dispersed in a liquid dispersion medium and which reversibly changes from a liquid state to a solid state due to its rheological properties when the shear stress or shear rate thereof increases to rapidly increase the viscosity.
The shear thickening fluid is usually in a liquid state, and changes to a solid state when a sudden shock is externally applied thereto. Due to this property, studies focused on impregnating the shear thickening fluid into fibers to provide bullet-resistant or stab-resistant materials are currently being actively conducted.
The shear thickening fluid is generally prepared as a sol-type dispersion or suspension by mixing nano-sized silica particles as solid particles with the polar solvent polyethylene glycol as a dispersion medium. In order to bullet-resistant or stab-resistant performance using the shear thickening fluid, it is required to increase the rate of filling of inorganic particles in the shear thickening fluid or the rate of impregnation of the shear thickening fluid in fibers. If the rate of filling of inorganic particles or the rate of impregnation of the shear thickening fluid is increased as described above, there will be a problem in that the impregnated shear thickening fluid flows down to form an agglomerate to thereby greatly reduce rather than increase bullet-resistant performance.
In addition, because the shear thickening fluid is in a liquid state, the use thereof alone may be limited, and the shear thickening fluid will be likely to flow down with the passage of time when it is impregnated into fiber. In addition, when the shear thickening fluid is mixed with a polymer material to prepare a composite, the uniformity of distribution of the shear thickening fluid can decrease. For these reasons, there is a need for studies to solidify the shear thickening fluid so as to widen the range of application thereof and process the shear thickening fluid so as to be uniformly distributed throughout a polymer complex.